1. Field of the Invention
The present invention relates to a lock nut having a high anti theft performance in which a fastening operation and a loosening operation can not be carried out by a normal general-purpose tool or a general tool, in a nut used in various fields in addition to a lock nut of a wheel for a motor vehicle.
2. Description of the Related Art
A lot of lock nuts in which a fastening work and a loosening work can not be carried out without using a special purpose tool have been proposed for various fields, and have provided for an actual use. For example, in order to prevent the theft of motor vehicle wheels, there has been proposed a lock nut which can be rotated only by a pair of special purpose tools (refer to Utility Model No. 3125160).
In addition to a performance for preventing the theft, a durability against a rust or the like is necessary for this kind of lock nut, and it is an object to improve them.